This invention relates to a survey marker which may be driven into a vertical surface while providing a horizontal reference surface, thereby facilitating EDM (Electronic Distance Measurement) surveying.
Traditional surveying methods employed survey markers placed in horizontal surfaces so that a transit could be set up over the marker. A plumb bob was normally used to center the surveyor on the mark; a dimple in the marker defined the exact center location. More recently, an optical plumb has been used as well as a mechanical plumb.
In more modern surveying, field measurements are obtained using EDM instruments. A typical EDM instrument emits a light beam which reflects from a distant prism (generally mounted on a prism pole) and then back to the EDM. This arrangement replaces the transit and rod of traditional surveying. In particular, if the dimple of a survey marker is located on a horizontal surface, a prism pole may be placed in the dimple and held vertically. Reflecting the beam from the prism on the prism pole serves to define an exact horizontal and vertical location.
However, presently available survey markers may be used with EDM instruments and prism poles only when the marker is placed in a horizontal surface, since only then is the dimple disposed horizontally. Often a location in a horizontal surface is not permanent; for example, if the marker is driven into the earth at a construction site, the location may be destroyed during construction activities. Fixing the marker in the earth is sometimes difficult because the ground is swampy, or covered with water or snow.
Accordingly, it is preferable in many instances to fix the survey marker to a vertical surface. Furthermore, it is desirable that the survey marker be inexpensive, since several markers are permanently left at the site in a typical surveying job.
U.S. Pat. No. 5,062,753 describes a survey nail which may be driven into a vertical surface. This nail includes two spike shanks and an integral benchmark surface which is horizontal when the nail is driven into the vertical surface. This arrangement has a complicated structure which increases its manufacturing cost. In addition, the patent describes a sighting dimple located on an impact surface of the nail. Such a dimple would be on a vertical surface when the nail is driven into a vertical surface, and thus would not be usable with a prism pole.